1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has scan and data electrodes for controlling the emission of electrons from electron emission regions.
2. Description of Related Art
Generally, electron emission devices are classified into those using hot cathodes as an electron emission source, and those using cold cathodes as an electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface conduction emitter (SCE) type.
An FEA type electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as the electron emission source, electrons are easily emitted from the electron emission source when an electric field is applied thereto under the vacuum atmosphere. A sharp-pointed tip structure based on molybdenum (Mo) or silicon (Si), or a carbonaceous material such as graphite has been applied for making the electron emission regions.
In a common FEA type electron emission device, cathode and gate electrodes are arranged on a first substrate perpendicular to each other in an insulating manner, and electron emission regions are provided on the cathode electrodes at the respective crossed unit pixel regions thereof with the gate electrodes. Phosphor layers and an anode electrode are formed on a surface of a second substrate facing the first substrate.
One of the cathode and the gate electrodes functions as a scan electrode, and the other electrode functions as a data electrode for carrying image data. The anode electrode receives a high voltage (a direct current voltage of several hundred to several thousand volts) required for accelerating the electron beams, and keeps the phosphor layers in a high potential state.
When scan signals are sequentially applied to the scan electrodes, and data signals are selectively applied to the data electrodes corresponding to the selected scan electrodes, electric fields are formed around the electron emission regions at the unit pixels where the voltage difference between the two electrodes exceeds a threshold value, and electrons are emitted from those electron emission regions. The emitted electrons are attracted by the high voltage applied to the anode electrode, and collide against the corresponding phosphor layers to thereby light-emit them.
The scan electrode is commonly formed with a metallic layer having a thickness of several thousand angstroms (1 Å=10−10 m), and receives a voltage of about 80V-120V during the driving of the electron emission device. When an electric current is applied to the scan electrode, heat is generated at the scan electrode due to the internal resistance thereof. Moreover, the scan voltage is applied as a rectangular wave pulse. The rectangular wave pulse has an advantage of uniformly causing emission of electrons from the electron emission regions, but it induces a temperature elevation at the scan electrode. This temperature elevation is due to the peak value of the instantaneous current increasing due to the instantaneous voltage application.
The generated heat deteriorates the scan electrode, and in a serious case, the scan electrode can become partially burnt out, and cut. The cutting of the scan electrode causes image distortion during the driving of the electron emission device.
To address this problem, it has been proposed that the scan driving pulse should be distorted to lower the peak value of the instantaneous electric current. Although this may reduce the heat generated at the scan electrode, a serious luminance difference may result between the left and the right sides of the screen, corresponding to both ends of the scan electrode during the driving of the electron emission device, thereby deteriorating the display quality.